What size are Ropp caps?
Apr. 18, 2025
ROPP Roll-On Pilfer Proof caps are aluminum screw caps applied to bottle necks using a roll-forming process, creating a tamper-evident and resealable seal. These caps typically range in diameter from 18 mm to 38 mm, covering standard neck sizes such as 18 mm, 20 mm, 22 mm, 25 mm, 28 mm, 30 mm, 31.5 mm, and 38 mm.
The height of the caps varies according to design requirements, ranging from 12 mm for miniature bottles to 60 mm for deep-drawn wine and beverage bottles. Typical heights include 12 mm, 15.5 mm, 18 mm, 24 mm, and 60 mm.
ROPP caps are made from medical-grade aluminum sheets with a thickness of 0.18-0.20 mm. They come with tamper-evident bands and offer liner options such as PVC, Tin Saran, and Sarannex to ensure effective sealing.
What is an ROPP Cap?
ROPP stands for Roll-On Pilfer Proof, referring to a cap where threads are formed directly on the bottle using pressure and rolling tools, rather than being pre-cut into the cap.
This process ensures a tight seal, and a tamper-evident band is left on the bottle neck upon first opening.
Due to their cost-effectiveness and compliance with regulations, ROPP caps are widely used in industries such as water, soft drinks, beer, wine, spirits, pharmaceuticals, edible oils, and agrochemicals.
Standard ROPP Cap Diameters
Common diameters: 18 mm, 20 mm, 22 mm, 25 mm, 28 mm, 30 mm, 31.5 mm, 38 mm, 46 mm, and 53 mm.
| Size Specification | Application Fields | Inner Diameter Range (mm) | Height Range (mm) |
| 22 mm Aluminum ROPP Caps | Pharmaceuticals, Food Industry | 22.0 (Standard Nominal) | 14.7 to 15.5 |
| 25 mm Aluminum ROPP Caps | Wine, Spirits | 25.1 to 25.5 | 16.1 to 16.9 |
| 31.5 mm Aluminum ROPP Caps | Beverages, Pharmaceuticals, Edible Oils, Special Purposes | 31.5 (Standard Nominal) | Regular up to 44, Special up to 60 |
Height Variation
Heights generally range from 15 mm to 60 mm, depending on the type and application of the cap. For example:
| Dimensions (mm) | Type | Common Application Scenarios |
| 28 × 18 | Aluminum ROPP Cap | Medical bottles, beverage bottles (such as mineral water bottles, functional drink bottles) |
| 31.5 × 44 | Aluminum ROPP Cap | Oil containers (such as olive oil bottles), chemical containers |
| 38 × 18 | Aluminum ROPP Cap | Sparkling wine bottles (such as champagne), industrial product caps (such as special liquids) |
Haomei Aluminum ROPP Caps Standard Dimensions
Aluminum ROPP Caps Diameter Sizes
- 18 mm
- 20 mm
- 22 mm
- 24 mm
- 25 mm
- 28 mm
- 30 mm
- 31.5 mm
- 38 mm
Aluminum ROPP Caps Height Sizes
- 12 mm
- 13 mm
- 15.5 mm
- 17 mm
- 18 mm
- 19 mm
- 21.5 mm
- 22 mm
- 24 mm
- 60 mm
Customizable Options for Aluminum ROPP Caps
Haomei Aluminum provides customized sizes, with diameters up to 38 mm and heights up to 60 mm. Customization options include embossing, debossing, or glitter coatings for brand identification.
- Printing and Surface Treatment: Offers offset printing, embossing, debossing, glossy varnish, and customized colors.
- Special Shapes: Variants with long, medium, and short skirt edges; pourer fittings for 31.5 mm bottle necks; deep-drawn caps with higher heights.
- Custom Sizes: Manufacturers can produce non-standard diameters and heights according to customer requirements to meet unique bottleneck specifications.
Industry-Specific Sizes for Aluminum ROPP Caps
| Industry Field | Common Dimensions (mm) | Feature Description |
| Pharmaceutical Industry | Diameter 18–22 mm | Smaller diameter, typically designed with tamper-evident features to ensure product safety and compliance |
| Beverage Industry | Diameter 28 mm, 31.5 mm | Larger diameter, suitable for carbonated drinks, functional beverages, etc., typically paired with sealing liners to enhance sealing performance |
| Spirits and Wine Industry | Diameter 25 mm, 31.5 mm | Suitable for high-end alcohol packaging, paired with EPE (expanded polyethylene) or LDPE liners for airtight sealing |
Aluminum ROPP Caps Standards and Tolerances
| Cap Size (Nominal Value) | Inner Diameter (ID) Range | Outer Diameter/Knurling Diameter (OD) or Range | Height Range (mm) | Dimensional Tolerance Description |
| 31.5 mm | 31.1 – 31.5 mm | Generally 31.5 ± 0.2 mm | 17.5 – 18.3 mm | Tolerance range ±0.1 – ±0.3 mm |
| 28 mm | — | Knurling Diameter 28.4 ± 0.2 mm | 17.5 – 18.3 mm | Tolerance range ±0.1 – ±0.3 mm |
Aluminum Ropp caps Summary Table of Key Sizes
| Diameter (mm) | Common Height (mm) | Applications |
| 22 | 14.7–15.5 | Pharmaceuticals, cosmetics |
| 25 | 16.1–16.9 | Wines, spirits |
| 28 | 15.5–18.0 | Beverages, medical |
| 31.5 | 17.5–44.0 | Oils, pharmaceuticals |
| 38 | 15.7–16.5 | Industrial, sparkling wines |
Aluminum ROPP Caps Material and Structure
- Aluminum Plate Thickness: Made from medical-grade aluminum with a thickness of 0.18-0.20 mm, balancing formability and strength.
- Tamper-evident Band: Features a separable skirt that remains attached to the bottle neck after the first opening.
- Liner Options: Includes PVC composites, PE, and EPE liners, suitable for cold filling, hot filling, and carbonated beverage applications.
- Forming Process: Threads are rolled onto the bottle neck using a specialized ROPP capping machine, equipped with adjustable heads to accommodate different diameters and heights.
Aluminum ROPP Caps Applications and Compatibility
ROPP caps are ideal for applications with high requirements for product integrity and tamper evidence. Common applications include:
- Beverages: Water, soft drinks, beer, wine, energy drinks.
- Spirits and Liquors: Whiskey, vodka, rum, cognac brandy.
- Pharmaceuticals and Healthcare: Syrups, oral liquids, dietary supplements.
- Food and Technology: Cooking oil, sauces, agricultural chemicals, lubricants.
Industry Bottle Neck Specifications Codes
- MCA2 (18 mm): Commonly used for mini liquor bottles and mixing bottles.
- MCA3 (30 mm): Standard specification for wine and beverage bottles.
ROPP caps provide a versatile, secure, and customizable capping solution for various liquid packaging applications, balancing performance and brand image.
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